Field of the Invention
The present invention relates to a dispenser suitable for dispensing a two-component spray polyurethane foam systems that are free of gaseous blowing agents.
Introduction
Dispensing devices for fluid components are in wide use for application of mixed fluids, especially in the area of polyurethane systems such as polyurethane foam systems. Two component polyurethane (2C-SPU) foam formulations are typically applied by simultaneously feeding an isocyanate component (A Component) with a polyol component (B Component) to create a mixture and then spraying the mixture from a dispenser.
2C-SPU foam systems are generally classified into two classes: those that contain a gaseous blowing agent (GBA) in one or both of the A and B Component and those that are free of GBA in either A or B Component (“GBA-Free 2C-SPU foam systems”). GBAs are blowing agents that have a vapor pressure greater than 0.23 Mega Pascals (MPa) at 25 degrees Celsius (° C.). Typical GBAs include 1,1,2,2-tetrafluoroethane (HFC-134a), carbon dioxide, nitrogen, and 1,3,3,3-tetrafluoropropene (1234ze). GBAs are beneficial in a 2C-SPU not only as frothing aids but to lower the viscosity of the component they are in. Lower viscosity components are easier to dispense because they require less pressure to flow through flow channels of a dispenser.
GBA-Free 2C-SPU foam systems generally require a pressurized gas as a third feed concomitant with the A and B components when dispensing the 2C-SPU foam system. GBA-Free 2C-SPU foam systems can be high pressure systems or low pressure systems. In high pressure systems, which are systems that require dispensing pressures greater than 4 Mega Pascals (MPa), the pressurized gas helps shape the spray and can be used to clean the dispensing nozzle used to dispense the 2C-SPU. In low pressure systems, which are systems that can be dispensed at pressures lower than 4 MPa, typically lower than 2 MPa, the pressurized gas is useful as a motive and mixing force for the A and B components. The requirement of a pressurized gas means that a dispenser requires at least three simultaneous feeds as opposed to two feed for 2C-SPU foam systems containing GBA. Additionally, the lack of GBA means that the A and B components are typically higher viscosity than in 2C-SPU foam systems containing GBA, which means the dispenser requires higher pressures, larger feed channels or both.
There are a number of dispensing devices suitable for 2C-SPU foam systems comprising GBAs. For example, particularly useful dispensing devices are disclosed in U.S. Pat. No. 4,925,107, U.S. Pat. No. 5,529,245 and U.S. Pat. No. 6,991,185. Each of these dispensing devices benefit from use of a spool valve that comprises a spool that conveniently can be repeatedly rotated between a closed-configuration and an open configuration by either squeezing or releasing a trigger. The spool has a pair of flow passage extending through it. In the open-configuration these flow passages in the spool align with flow passages in component feed channels of the dispenser so as to allow A and B Components to flow through the spool and ultimately out of the dispenser. In the closed-configuration the flow passages rotate out from alignment with the feed channels of the dispenser thereby precluding A and B Component to flow. Such a dispenser is designed for 2C-SPU foam systems that contain GBA, systems that require two feeds and have relatively low viscosity fluids. However, dispensers well suited for 2C-SPU foam systems containing GBAs are not necessarily well suited for use with 2C-SPU foam systems that are free of GBAs due at least in part to a need to dispense higher viscosity A and B Components as well as simultaneously dispense a pressurized gas with the A and B Components.
Dispensers taught in the references cited above are unsuitable for use with GBA-Free 2C-SPU foam systems. GBA-Free 2C-SPU foam systems require at least three dispensing fluids that simultaneously combine as they are dispensed. The dispensers described above allow for only two fluid feeds. Adding a third fluid feed to a spool valve type dispenser in a manner that does not leak—which is a critical requirement for reactive systems like 2C-SPU foam systems—is non-trivial. Similarly, engineering a suitable dispenser that can operate with higher viscosity A and B Components is non-trivial because it requires operating at higher pressures, larger diameter feed lines, or both and any one of these requirements creates challenges for designing a valve system on the dispenser that functions in an convenient manner without leaking and that is inexpensive to manufacture.
There is a need for a dispensing device suitable for use with GBA-Free 2C-SPU foam systems. In particular, there is a need for a convenient and inexpensive dispensing device that can accommodate the A and B Component viscosities of a GBA-Free 2C-SPU foam system along with a third gas feed and that provides impingement of the three feeds as it dispenses while avoiding leaking and premature mixing of A and B components in the dispenser. Moreover, it is desirable to use a convenient and inexpensive spool valve type actuator in such a dispensing device to make assembly and operation simple and cost low.